In the art of impact crushing, solid particles are carried by a gas stream and are disintegrated into a plurality of smaller particles of correspondingly lower weight due to impact on an impact surface.
EP 0300402 B1 pertains to the generation of extremely small particles in such a way that the particles to be crushed, which already have a relatively low weight, are first suspended in a fluid. The fluid with particles suspended in it is then accelerated and caused to impact on a surface with increased energy. To accomplish this, drop-like portions are taken from the suspension and are, in turn, caused to impact on the surface. This type of impact crushing is based on the consideration that the crushing of particles can be successfully achieved only if the weight of the particles to be crushed is not lower than a certain minimum value. If the weight of the particles to be crushed is too low, there is a the risk that they do not impact on the impact surface at all, but are drawn off with the fluid stream in front of the impact surface, or they, at best, impact on the impact surface with a very low energy and are then deflected to the side, with the suspension, and guided parallel to and along the impact surface.
It has been proposed that the solid particles to be crushed should not be simply suspended in a fluid, and the suspension thus formed should not be caused to impact on the impact surface but, instead, that the solid particles should be suspended in a first fluid, after which droplets should be formed from this suspension, and each droplet should consist of a fluid component containing, at most, only a few solid particles. Each of these droplets is separated from the respective other droplets of the same type, and the mass of these droplets is in turn carried by a carrier fluid stream and caused to impact on the impact surface. Instead of individual solid particles, which are directly carried by a carrier fluid stream and can be caused to impact on the impact surface only insufficiently because of their low weight, and are crushed correspondingly insufficiently, each solid particle is consequently first made the component of a droplet of higher weight, which is impacted with a substantially higher energy. Hence, even solid particles of extremely low weight can be further shattered as a consequence of the increased impact energy.
In practice, the first fluid is usually a liquid, and the second fluid, i.e., the carrier fluid, is a gas. The suspension of liquid and the solid particles of low weight is contained in a container, and a gas stream is blown with high energy into this container and consequently into the suspension. The gas stream carries droplets consisting of portions of liquid and solid particles suspended in it and impacts them in the manner described.
The foregoing leads to two different possibilities for achieving impact crushing.
The first possibility is, to a large extent, the above-described technique, in which the portion of suspension consisting of liquid droplets and solid particles contained in it in the smallest possible number, which portion of suspension is carried by a gas stream, is caused to impact on an impact plate.
The second possibility is a modification, in which a plurality of high-energy gas jets directed opposite each other are blown into the container containing the suspension, i.e., the impact crushing is performed by means of at least two portions of suspension accelerated against each other.